Abstract: In semantirbased query expansion, computing expansion words and its weight is a key step to describe the needed query. We proposed a method called OLCA (keyword to concept method) , the idea comes from LCA(Local context analysis). We made some improvement and applied it to multi-keywords ctuery with different weight according to their attribute to the query. Combined with concept tree based on WordNet, we made the query expansion performed from both semantic and the real ctuery documents aspects, and calculated the weight of expansion term based on this technique. Compared with the one based on semantic or the traditional expansion which merely is based on statistic, the experiments reveal that this method can achieve a better query quality.

Key words: Multi-keywords, Query expansion, Concept tree, Local context analysis